The present invention relates to loaders for conveying signatures and the like.
There are already known loader devices for conveying or transporting signatures.
The known devices generally comprises an supporting frame housing a horizontally extending path for feeding the signature packs which are then raised along another path, the feeding and raising paths consisting of belts or the like extending between driving and driven rollers. Above the raising path there is provided a raising frame, which latter consists of a belt extending about pulleys in such a way as to suitably arrange the signatures. The raising frame is longitudinally movably supported, in order to fit with signatures of different size. This construction is known for example from the U.S. Pat. No. 3,894,732.
In the known signature loaders it occurs that on the first signatures near the raising path and in particular on the leading signature, a very high pushing force is exerted, which, on one hand, is due to the weight or the signatures themselves, which are slightly forwardly slanted and, on the other hand, it is due to the entraining action on the signature pack exerted by the conveyor belts.
Thus a rather high friction occurs, in particular with respect to the first signatures, as well as between the first signature sheet contacting the raising path, which path subjects the first signature sheet to a drawing action, and the last sheet of the first signature, which is pressed by the pack located downstream, so that the first signature, that is the leading one, tends to slip away on the last sheet held by the feeding pack. Thus there occur the so-called "autoexfoliation" phenomena of the signatures, which phenomena are more intense when the signatures comprise a great number of sheets, which number may amount to 60-70 pages and more.
In order to overcome the drawback mentioned hereinabove, it has been proposed to provide, at one end of the horizontally extending feeding path, a short portion of slanted feeding, capable on one hand, of slightly reducing the pushing force due to the pack weight, by slanting in front in a greater amount the signatures, and, on the other hand, capable of further reducing the pushing force, by discharging a portion on the first driving or transmission roller.
In actual practice it has however been found that the mentioned approach does not permit the signature conveying problem to be efficiently solved, in particular in the case of signatures difficult to handle, such as the illustrated magazine signatures, or the signatures including a a great number of sheets, and in the case of signatures open on at three sides.
Moreover in the known loaders, operation unevennesses occur because of the different friction exerted on the signatures depending on the paper type and the printing marks, in a single colour or in multiple colours, as well on the spreading on the signature of the printed zones.
The operation unevennesses mentioned hereinabove generally consist of a bad drawing or the signatures from the signature pack, so that the signatures are erroneously located on the conveyor belts, with the consequent requirement of intervention by the operating personnel. Moreover the known loaders may hardly be fitted to different sizes of signatures.
Still another drawback of the known signature loaders is that they require mechanical elements for preadjusting the signature pack at the raising zone since, by way of an example, in the case of the so-called bound signatures or signatures provided with three open or cut sides, the front portion of the signature pack, upon breaking the binding element, which generally consists of a plastics strip, tends to assume a misaligned fan shape, so that the signatures are conveyed to the raising pulleys with an uneven arrangement susceptible to cause the signatures to move in an erroneous slanted direction.